Prognostic role of slow vital capacity in amyotrophic lateral sclerosis.

Objectives: To compare the prognostic role of FVC and SVC at diagnosis in amyotrophic lateral sclerosis (ALS) patients.
Methods: We included all patients from the Piemonte and Valle D'Aosta ALS register (PARALS) who had been diagnosed with ALS between 1995 and 2015 and underwent spirometry at diagnosis. Survival was considered as time to death/tracheostomy; to assess the prognostic value in typical trial timeframes, survival at 12 and 18 months was calculated too. Cox proportional hazard regression models adjusted by sex, age at diagnosis, diagnostic delay, onset site, and ALSFRS-R total score at the moment of diagnosis were used to assess the prognostic role of FVC and SVC.
Results: A total of 795 ALS patients underwent spirometry at diagnosis during the study period. Four hundred and sixteen (52.3%) performed both FVC and SVC, whereas the others performed FVC only. FVC and SVC values were highly correlated (r = 0.92, p < 0.001) in the overall population and slightly less correlated in patients with bulbar onset (r = 0.86, p < 0.001). Both FVC and SVC proved to have a prognostic role with comparable hazard ratios (HRs) (HR 1.83, 95% CI 1.48-2.27 and 1.88, 95% CI 1.51-2.33, respectively). When considering typical trial timeframes, HRs remained similar and were inversely proportional to FVC and SVC values.
Discussion: FVC and SVC at diagnosis can be used interchangeably as independent predictors of survival in both clinical and research settings.